Many radio pagers are small portable devices carried by individuals. Since they are portable devices, pagers carry a battery power source requiring replacement or recharge. In order to avoid frequent charging it is desirable that pager radio receivers be power efficient.
In U.S. Pat. No. 4,713,808, issued Dec. 15, 1987 to Gaskill, et al., pager power consumption is greatly reduced by a transmission protocol wherein radio receivers of individual pagers are only active during predetermined time slots. The broadcast stations which transmit messages are programmed to broadcast message data for a each pager during the time slots associated with that pager.
Transmission protocols, such as the above described Gaskill system, necessarily use a monitor interval longer than the associated time slot to compensate for unpredicted timing errors or inaccuracies. A longer monitor interval increases the probability that the radio receiver will be turned on to capture radio transmitted message data during the associated time slot. Since the monitor interval is longer than the time slot, the radio receiver is on for a time before the associated time slot. Such additional radio receiver on time contributes to inefficient power consumption. It is, therefore, desirable that the monitor interval be long enough to reliably receive message data, yet short enough to improve power conservation.
As the operating environment for each pager changes, its timing circuitry is affected and its timing or synchronization capability is thereby degraded and a monitor interval longer than the associated time slot is necessary. More particularly, to maintain high message reliability, it has been necessary to initiate the monitor interval in advance of the target time slot to accommodate a broad range of potential variations in environmental conditions through the lifetime of the pager. At one extreme of this range, prevailing environmental conditions cause the monitor interval to begin just before the target time slot. At the opposite extreme, prevailing conditions cause initiation of the monitor interval long before the target time slot. Such conservative measures taken to insure message reliability, however, contribute to excess power consumption.